Method of transmitting signals



March s. GUANELLA EI'AL 2,312,897

METHOD OF TRANSMITTING SIGNALS Filed Oct. 9, 1940 5 Sheets-Sheet l Mar2, 1 G. GUANELLA EI'AL.

METHOD OF TRANSMITTING S IGNALS 5 Sheets-Sheet 2 Filed Oct. 9, 1940 /5 fZ-A? ch 2,1943. cs. GUANELLA EI'AL 2,312,397

METHOD OF TRANSMITTING SIGNALS Filed Oct. 9, 1940 5 SheetsSheet 3 G.,GUANELLA ETAL METHOD OF TRANSMITTING S IGNAL5 5 Sheets-Sheet 4 FiledOct. 9, 1940 March 2, 1943.

G. GUANELLA ET AL METHOD OF TRANSMITTING SIGNALS 5 Sheets-Sheet 5Patented Mar. 2, 1943 METHOD OF TRANSMITTING SIGNALS Gustav Guanella andWalter Ernst, Zurich,

Werner Lindecker, Ennetbaden, and Marcel Gabriel, Baden,

Switzerland, assignors, by

mesne assignments, to "Patelhold Patentverwertungs-& Elektro-HoldingA.-G., Glarus, Switzerland, a joint-stock company Application October 9,1940, Serial No. 360,516 In Switzerland July 14, 1939 20 Claims. (01'.179-15) According to the known systems and arrangements for thetransmission of signals, these are distorted at the transmitter end soas tov render them unintelligible to unauthorised receivers. Thereceived signals can then be freed from'this distortion by means ofcorrespondingly adjusted devices so that they can be understood by the vauthorised receiver.

This distortion can be made particularly effective if the sequence ofcertain parts of the signal is altered in accordance with a definiteprogram. This scrambling of the time sequence of the signals can beachieved in a known manner by means of a switching-over device whichtransmits the signals in a constantly recurring sequence over variousparts of a time-delay device, these parts being characterised by unequalretardation times. The individual signalling elements a, b, c, d theduration of which To corresponds to the constant distance between twocontacts of the switching device, are therefore retarded by the at leastpartly difierent times ta,

ts, to ,so that with a suitable choice of retardation times the newsignal b, d, a, c, can for instance be formed.

The program for this scrambling repeats itself after each revolution ofthe switching-over device; that is to say each group of n elements theduration of which T1 corresponds to a complete revolution of theswitching-over device, is scrambled in the same manner. By means of asimilar apparatus operating in synchronism, the elements of the receivedsignal are again retarded so that the total retardation time Tz-is thesame for each element. In this manner the original sequence of elementsis restored and the signals are received free from distortion but with atotal retardation Tz.

For constructional reasons the number of switch segments which thechange-over switch can accommodate is limited, and therefore the numberof elements 11. per group is also restricted. It is thus possible thatan unauthorised receiver by means of systematic trials may discover thescrambling key in a comparatively short time by rearranging the receivedsignals according to the deciphered part of the signal consisting of 'nelements. Since the scrambling program repeats itself after each groupof n elements the complete message can thus be deciphered.

This disadvantage ofthe known systems and arrangements is avoidedaccording to the invention whereby before transmitting the intermediatesignals resulting from a first scrambling of the elements in accordancewith a first partial program which repeats itself after time intervalsT1, these intermediate signals are scrambled a second time according toat least one further partial program which repeats itself afterdifierent intervals of time. transmitted message must first bedeciphered to obtain the last intermediate signal formed at thetransmitter end and from this by means of at least one furtherdeciphering the original message is finally obtained. This new method ofscrambling and the apparatus required are ex plained by means of theconstructional examples illustrated in Figs. 1-5 of the accompanyingdrawings in a diagrammatic manner.

Since with the method of multiple scrambling already briefly describedand formingthe subject of the present invention, the various partialscrambling programs repeat themselves after unequal periods of time,this multiple scrambling is effected according to a complete programwhich repeats itself after a time which is greater than the sum of therecurring periods of all the partial programs. If each scrambling isefiected with elements of equal length the various partial programs mustobviously be based on groups having an unequal number of elements. It isadvisable to select numbers for the elements which are not mutuallydividable. A first partial program having groups containing m elementsand a second partial program with groups of n elements all equally long,when used one after the other for multiple scrambling, result in acomplete program which repeats itself only after mxn elements because itis only after the lapse of m n elements that the beginning of eachpartial program coincides again.

An alteration in the first partial program cannot be compensated byaltering the second partial program in order to maintain the samecomplete program, because both partial programs always recur atdifferent times. For the same reason a mistake in the program of thefirst partial diciphering cannot be continuously corrected by alteringthe second partial deciphering; that is to say faultless completedeciphering is only possible when the intermediate signals obtainedafter partial deciphering exactly correspond to the intermediate signalsat the transmitter end. Since the intermediate signals are,

however, still in cipher, that is to say represent an unintelligiblemessage, the correct intermediate signals at the receiving endcorresponding to the intermediate signals at the transmitter end are notsuch that they can be understood. It is therefore impossible todetermine the "correct" At the receiving end the intermediate signalsand subsequently the original message from the received signals merelyby systematic trials. Unauthorized deciphering of received signals bymeans of systematic trials is therefore rendered extremely diflicult.

Under certain circumstances it may, however, be possible bysystematically altering the various receiving keys to obtain anintelligible series of elements from the received signals, whereby thenumber of such elements does not exceed the number of elements pergroup. This temporary deciphering of a' short series of elements canoccur as a result of an exceptional coincidence of entirely incorrectpartial deciphering programs which produce incorrect intermediatesignals. Such a coincidence repeat itself after passing through thecomplete scrambling program. In the example given above where there is adouble scrambling in groups of m and n elements, temporary decipheringof a short series of elements would recur only in comparativel largeintervals of m n elements. Conditions for unauthorised decipherlng areconsiderably more unfavourable if a large number of single scramblingsare used. For instance, four successive individual scramblings in groupscontaining 9, 10, 11 and 13 elements result in a total scramblingaccording .to a program which repeats itself only after 9X10X1113=12,870 elements. .A'

temporary correct deciphering. of sabout 10 ele-. ments attainedbytrials, which repeats itself at intervals of more than 10,000,. cannotserve .to

render the sense or contents of the completemesj sage in any wayintelligible. A special advan tage of thenew method is that thesuccessive individual scramblings can be performed in groups having asmall ,numbero'i' elements and short is considerably smaller than thatrequired for the simple scrambling systems used hithertmdespite the factthat a much higher degree of secrecy is achieved.

The drawings illustrate the invention, showing several modifications andapplications thereof. In the drawings:.

Fig. 1 shows a transmitting device and receiving device according to theinvention;

Figs. 2 to 5 show circuits for sending and receiving multiscrambledsignals; s

Fig. 6 shows the fundamental system of connections for a scramblingdevice;

Fig. 7 shows a special construction of scrambling key;

. Fig. 8 shows a scrambling device provided with a steel tape time-delaydevice;

Figs. 9 to 11 show circuits for sending andvreceiving scrambled signalswith the device of Figs. 6 to 8;

Fig. 12 shows a scrambling device having a single signal carrier and twoswitch elements;

Fig. 13 shows in detail a device similar to that shown in Fig. 12;

Fig. 14 shows a modified form of the apparatus of Fig. 13; and

Fig. 15 shows a circuit for two scrambling devices, as shown in Fig. 12,and an amplifier.

In the constructional example illustrated in Fig. 1 of the drawings S1,S2, S3 represent three ciphering devices at. the transmitting end andE1, E2, E3 the corresponding deciphering devices at the receiving end.These devices are equipped with retarding mean the delay times of whichare altered by the change-over devices U1, U2, U3, V1, V2, V3 in aperiodically recurring succession is obtained again. i

that is to say,-the first element is brought into the second place ofthe same group and the third element into vthe'first place of the nextgroup. so that from the original signal Zo=abcdejghiklmn0pthe firstintermediate signal Zi=-acdbfyeikhmnlp-ois formed. The second cipheringdevice 5: with the tour-contact switch U: operates for instance inaccordance with the key number ment into the first place of the nextgroup and so on, so that the second intermediate signal Zz=-'-- adcfbegkimhln-p -o is formed. Inv accordance with the keynumber I .ll" P=41532 a further and"final scrambling in'groups of five elements isaccomplished byvmeans'of the switch device S3 in order to'produce thesignal I 3=' F fii. a T d if c e b'QTi IC-jhn l-n p p 9 to be alarmed.This s gnal is forinstance transmitted through the channel L. At thereceivingend the first deciphering device E1 with the five-step switchV1 scrambles, the transmitted signal Z3 according to a key numberQ.=2541-3 i which is associated with the partial program, Pa on thetransmitting'side, and thus producesthe second intermediate signal t 2z=r a d c f bjei-g k i m hi a-epic Then according toja further key numbera which i assoclated with the ke instigate the transmitting side andhappens with it, the first intermediates'ignal.

Z1=-'a-cdbfgeikhmnlp 'o-c is produced by the device E2 from theintermediate signal Z2. Finally with the device E: and the key number tocoincide Zo=-abcdefghi]clmnap With this arrangement the transmitting andreceiving end associated with each other,namely U1 and Va,U2 and V2,U:and V1 operate in synchronism and the change-over from one segment tothe next always occurs at the: If the change-over switches are sameinstant. of the mechanical type they can be actuated by two synchroniseddriving apparatuses A and B switches at the provided with suitablegearing. The synchronisation can be achieved in any known manner:- forinstance, by employing a periodically transmitted synchronising impulse.Naturally the ciphering and deciphering with elements of constant lengthcan also be undertaken in such a whole multiple of the time of rotationof the other switch so the complete scrambling program only repeatsitself after intervals which are greater than the period of rotation ofeach individual scrambling device in the apparatus.

In systems arranged for transmission in both directions specialscrambling devices can be provided at each end for transmitting andreceiving, as shown in Fig. 2, where the equipment of station I isdesignated by the numerals ll, l2, etc. and that of station II by thenumerals 2|, 22, etc. The direction of the transmission is reversed bythe manually or automatically operated change-over .switch R. The switchpositions shown in full lines apply to a transmission from station I tostation II whilst the dash lines indicate the positions when thedirection of transmission is from II to I. The switches can also bereplaced by fork connections or alternatively separate connections canbe used for both direc:- tions oftransmission.

The arrangement illustrated in Fig. 3 indicates I how the samescrambling devices can be employed for both directions of transmissionwhen the signals to be scrambled and the received signals are passedthrough the scrambling devices in the same direction. In this case thecomplete scrambling keys for both directions of transmission do not byany means correspond to each other because for instance the keys for S11and $21 which operate with unequally long groups of elements cannotpossibly be associated. With the arrangement shown in Fig. 4 it is,however, posinstance a gramphone record and then picked up anddeciphered when desired. This new method is of course not restricted toscrambling spoken messages. Thesignals in question may also consist ofimpulses or tones such as are used in connection with telegraphy,teleprinting or other systems for the transmission of messages, ordersand the like.

The various apparatuses which it is preferable to use for thescramblingsystem according to the invention are now described in greaterdetail by means of a number of constructional examples which areillustrated diagrammatically in the accompanying drawings.

Hitherto in order to minimise the risk of unauthorised deciphering asmuch as possible it has been necessary either to have a very longretardation time or a short retardation time and a large number ofdifferent running periods for the time-delay device. This, however, is aconsiderable disadvantage and prevents direct communication in twodirectionssuch as is required for telephone services. It is thereforeone of the objects of the invention to provide a transmission systemwhich enables these disadvantages to be overcome and at the same timeguarantees that the possibility of the transmitted signals beingdeciphered by an authorised person is extremely remote, the retardationtimes being kept sible when reversing the direction of transmission alsoto reverse at the same time the sequence of the individual scramblingdevices S11. $12 or E11, E12, so that for instance the firsttransmitting key operates in both directions of transmission withequally long groups. Since the key numbers associated with each other donot usually coincide, the complete scrambling programs for bothtransmitting directions will also not coincide.

The entire apparatus can also consist of a number of scrambling deviceswith reversible direction of transmission, as shown in Fig. 5. In

this event the complete scrambling programs co-' very short and thetime-delay device itself very simple. Furthermore in proportion to therunning period it is possible to obtain an extensive scrambling of thesequence in which the signal elements succeed one another. This isachieved by the use of. the following arrangement. The time-delay devicepossesses connections for m different running times, these difleringfrom each other by an integral multiple of I/nth the period of rotationof the switch. device and furthermore so dimensioned that the.diiference between the longest and the shortest running time is notgreater than (3n-1) times the duration of one period of rotation of theswitch device. The switch device is provided with n connections whichare periodically switched in one after the other and the number of whichis at least equal to the number of retarding times m. The scrambling keyis so constructed and located between the m connections of thetime-delay device and the 12 connections of the switch device that bymeans of the key each of the n connections of the switch device can beconnected as desired with the m connections of the time-delay device.

which, when the short switching intervals be-- tween two successivecontact segments are neglected, is equal to l/nth of the duration of onecomplete revolution of the switch arm 5. In the constructional exampleshown in Fig. 6 six contact segments are provided so that in this casen=6. The arrow shown on the switch device indicates the direction ofrotation of the switch arm 5. The contact segments 6 are connected bymeans of leads with the key 3 which latter consists essentially of anetwork comprising two groups of conductors. One of these groups ofconductors possesses n conductors which are connected as shown with thecontact segments 6 of the switch device 2. The other group possesses atthe most n conductors and in the example illustrated only conductorswhich lead to the terminals 1 on the time-delay device i. At the pointsof intersection of the conductors, contacts are provided by means ofwhich each conductor connected with the time-delay device I can beconnected with each conductor which leads to the switch device 2. If thenumber of conductors connected with the switch device 2 is indicated byn and the number of conductors connected with the time-delay device I isindicated by m, there will be nXm points of intersection and an equalnumber of contacts. The terminals on the retarding device are thusselected so that none of the m retardation times differs from theremaining Ones by the duration of a rotation of the switch device. It ispreferable if the m retardation times form an arithmetic series whereeach is greater than the preceding one by l/nth of a rotation of theswitch device. Furthermore it is expedient that the number ofretardation times should equal the number of contacts on the switchdevice which are successively switched in. Thus m is selected to beequal to n so that the key 3 has n contacts. In order to obtain afaultless transmission of the signal and to be able to adjust theciphering positions easi1y,.the scrambling key 3 comprises two groups ofconductors, the first group consisting of n conductors leading to theswitch device and the second group consisting of m conductors leading tothe terminals 1 of the time-delay device. These two groups of conductorsare arranged as already mentioned in the form of a network with mXnintersection points where contacts are provided,

as indicated by the circles shown in'Figs: 6 and 7. As shown in Fig. 6the n conductors which form the network lines in one directionand areconnected with the segments of the switch device,

are arranged within the ,range of the network in the order in, which thesegments 6 offthe switch device are successively switched in; Similarlythem conductors of the second group, which leadto the terminals I of'theretarding device a e arranged according to the graded running times. Ifthen (m nl') diagonals are drawn through the m n contacts, 'as indicatedby the dash-dot lines, the following conditions will be obtained wherebyall ciphers can be determined with which a faultless transmission of thesignal in question is possible. Exactly one single contact must beplugged in on each of the horizontal conductors leading to the switchdevice. Similarly there must be exactly one plugged-in contact on n ofthe (n+m-1) diagonals, whereby it should however be made impossible thatfor instance a contact is plugged in on the (n-l-x) diagonals countedfrom above when such a contact already exists on the :c diagonals, where:r is a whole number. It is therefore expedient to adopt specialmeasures, such as mutual mechanical interlocks, to prevent this andensure that the aforementioned rules. are adhered to. The scrambling keybecomes very simple and clear if it is constructed as shown in Fig. 7.Thearrangement shown in Fig. '7 is obtained from that shown in Fig. 6 bymeans of the following transformation: The arrangement of the individualcontacts shown in Fig. 6 is kept fixed and all contacts lying on the(n+1) to (1z,+m1) diagonals are displaced 21. contact spaces to the leftso that the original (n+:i:) diagonal now forms the continuation of thea diagonal. The aforeas follows. applied to the terminal 4 of the'switchdevice" tact must be closed on each of the resulting diagonals with mcontacts each and on each of the 1:. horizontal conductors leading tothe switch de-- vice. A complete key thus always consists of n closedcontacts.

Under the above conditions it is possible to employ the arrangementshown in Fig. 6 either for transmitting or receiving. Furthermore thereare two fundamentally difierent operating methods when it is assumedthat the direction in which the retardation of the signal elementsoccurs is always the same. This direction is indicated by the arrowshown on the time-delay device l of Fig. 6. The signal which is to beciphered can enter the apparatus at the terminal 9 and is first of allretarded. After being subjected to various retardation times thecomplete signal passes over the m terminals of the timedelay device Iand'over the scrambling key 3 to each of the contact segments 6 of theswitch device 2. At each of the contacts 6 the signal has a difierentretardation time,that is to say it reaches each of the contact segmentswith a difierent delay. The actual retardation times are determined bythe connections with the terminals I on the time-delay device I, whilstthe sequence of the retardations at the contacts 6 is determined by themanner in which key contacts are plugged in. The switch arm 5 of theswitch device 2 takes only I/nth of the signal at each of the contactsegments 6 so that the signal is divided into elements the duration ofwhich is.

which is being used. It is thus possible for signal elements which wereoriginally next to each j other to be so displaced that the interval oftime between them is equalto the difference-between the longest andshortest retardation time.

The second method of operating the appa-' ratus shown in Fig. 6 forscrambling signals is The message to be ciphered is first 2 and is thusfirst divided into equal elements which reach the terminals 1 of thetime-delay device according to the key used. The elements are thensubjected to the required retardation and are received at the terminalI]! in scrambled sequence. Faultless transmission is also assured inthis case if the conditions already referred to are fulfilled. It canalso be shown that these two methods of operation are also possible ifthe ciphered message is to be deciphered by means of the apparatus shownin Fig. 6. The scrambled signa1 can thus either be applied to theterminal 9 and received at the terminal 4 in deciphered form or appliedto the terminal 4 ciphered and received at l0 deciphered. Depending uponthe connection of the transmitter and receiver it may under certaincircumstances be necessary to plug in a different key'in the receiver,or change-over connections must be provided for the key which enablesthis change over to be accomplished automatically as soon as theapparatus has to operate as a receiver instead of a transmitter.Connections for the transmitter and receiver, which are particularlysuitable for intermittent both-way operation are described later bymeans of the arrangements shown in Figs. 9 and 10.

The construction of the key, time-delay device and change-over switch isnow described in greater detail. Th time-delay device I can consist ofan acoustic tube in which at the point 8 the signal to be transmitted istransformed into sound waves which at the terminals 9 after a certainrunning time are transformed back into electrical oscillations by meansof a microphone.

- It is also possible to arrange sound transmitters at the terminals 1-which send sound waves through the tube in the. direction indicated bythe arrow (Fig. 6). A microphone is then located at the point II whichconverts all the sound waves into electric oscillations. This acoustictime-delay can be replaced by a purely electric time-delay. For instancea large number of low-pass filters'connected in series can be arrangedbetween the terminals 8 and H, each terminal I being associated with adefinite number of these filters. The time-delay is then equal to therunning time through these filters. An acoustical or electricaltime-delay is, however, not very suitable for the scrambling deviceaccording'to the invention because it is difiicult to obtain thenecessary exact synchronous operation of the-switch device in relationto the different running times and to maintain this synchronism forlonger periods. It is therefore best if the time-delay device consistsof a mechanically actuated signal carrier on which the transmittedmessage is recorded and then reproduced after the required intervals oftime. The signal carrier can be a film on which the signals are recordedmechanically and reproduced photo-electrically. It is, however,preferable to use a device such as that shown in Fig. 8 where thetime-delay device comprises an endless steel tape I which is actuated bythe roller l2. The roller I2 is rigidly coupled to a driving motor l3and the gearing I4, which latter drives the switch device 2. A steeltape time-delay device oii'ers advantages because it is possible toremove the message from the tape very simply by means of a wiping headl5 after it has been delayed and to render the tape ready for a freshrecording without having to interrupt its motion. Steel tape time-delaydevices can either operate with two pole or single pole heads forrecording and reproducing the signals. It is, however, preferable toemploy single pole heads for the keying devices according to theinvention. The single pole heads both for recording and reproducing thesignals consist'of a coil surrounding a ferromagnetic pole piece whichis in sliding contact with the steel tape, as shown in Fig. 8. Thesepole pieces are so constructed that they can be used equally well forrecording or reproducing. When recording a message on the tape a directcurrent-source is connected in series with the magnetising coil so thatthe recording head is given the desired initial magnetisation. The heads1 shown in Fig. 8 then function either as recording or reproducing headsaccording to the direction of transmission forwhich the scramblingapparatus is connected.

The"head' 8' is'used solely for recording whilst the head II is employedonly for reproduction purposes, The distances between theheads Icompared with the speed 1 of the steel tape I are then fixed so that n'd'=v s p; n being the n'u'mber'of contacts on' t he switch device, 8'the duration of a rotation of the switch device and 1) any positivewhole number which for'the successive distances between the heads isexpediently selected to be equal to unity. The individual retardationtimes then form an arithmetic series.

The key 3 is constructed in the same manner as that shown in Fig. '7,the number of conductors connected to the switch device being equal tothe number of conductors leading to the t1me-delay device. In theconstructional example shown in Fig. 8 m is thus selected to equal n sothat the key 3 thus has n contact points, in. this case 16. Thearrangement shown in Fig. 8 diiiers from that in Fig. 7 in so far as theinclined diagonals of Fig. 7 are now arranged vertically and are omittedfrom Fig. 8 for the sake of clearness. The connections between thecontacts on the key and the time-delay and switch devices are, however,unchanged. For the practical construction of the key 3 it is preferableto provide it selector switcheseachhaving n contacts which are soarranged that all the contacts in one horizontal v linecan be switchedin one after the other in the desired order by the selector switches. Ifthe 71 positions on each selector switch are numbered in acontinuoussequence an index having n numbers will be obtained which characterisesthe selected key position. The aforementioned conditions thus show thateach number may only occur once in the index if the scrambling is to befree from errors. This system with selector switches is preferably alsoprovided with electro-magnetic relays which automatically wipe out thekey number as, soon as the scrambling device is switched out or if adisturbance occurs.

The switch device can also be constructed in a number of different ways.The mechanical switch contacts 6 can be replaced by electron tubesacting as switches. The switch 2 can also be designed as a capacityswitch, the segments 6 being fixed condenser plates and the condenserplate attached to the arm 5 being rotated close to the fixed plates thussplitting up the signal into individual elements. Coils can also beemployed instead of the contact segments 6, th coil axes being arrangedaccording to the switch axis. It is then possible to obtain an inductiveconnection by meansof a coil fixed to and moved by the arm 5. In themechanism described above it is preferable to replace the contactsegments 6 by cam operated switches each comprising two stationaryspring contacts which are switched in one after the other by means of arotating disc provided with a cam.

It is often required that an apparatus of the kind shown in Fig. 6 orFig. 8 should either be used to cipher a signal or to decipher ascrambled signal. Once the key has been plugged in it shouldremainunchanged for both cases, furthermore in order to obtain a shortchange-over time the direction of rotation of the signal carrier shouldremain the same. The change-over connections can be reduced to amini-mum if an additional recording head 8 is located in front of and anadditional reproducing head i i is located after the m reproducing andrecording heads 1 respectively, shown in the arrangement illustrated inFig. 8. The switching over of the apparatus is explained now by means ofthe arrangements shown in Figs. 9 and 10, where I and II are the sameapparatuses as these shown in Figs. 6 an'd8. For the sake of clearnessonly the relevant terminals l0, 9 and t are indicated. Both apparatuses,each of which can be used for operating in either direction, areconnected by means of a trans mission channel l6. This transmissionchannel Hi can consist of an ordinary wire conductor, for

instance a telephone cable, or sections of the transmission channelcanalso be operated by .wlreless means. Each apparatus I and II is forinstance equipped with a microphone il, a receiver i8 and a change-overdevice 19. In one end position of the change-over device the apparatusfunctions as a transmitter and in the other end position as a receiver.When the apparatus I and II is therefore being employed for intermittentboth-way transmission the change-over device for the one apparatuswillbe in one end position and the change-over device for the otherapparatus in the other end position. Under these conditions a number ofthe described apparatuses can be connected to the conductor I G if it isdesired to establish a multiplex system.

With the arrangement shown in Fig. 9 the change-over device it islocated on the terminals ii and iii and switches in either themicrophone it or the receiver 18 in the apparatus I and II. Thetransmission channel I8 is not changed over and lies between theterminals 6, that is between the switch devices of the apparatuses. Thearrows in Figures 9 and 10 indicate the course of the signals throughthe apparatus and the transmission channel. The single arrows indicatethat apparatus II is operating as transmitter and apparatus I asreceiver, whilst the double arrows show that apparatus I is operating astransmitter and apparatus II as receiver. In Fig. 9 when receiving, thechangeover device it causes the signal which is to be scrambled and isreceived by the microphone I! to be passed to the recording head infront of the m recording and reproducing heads Where it is recorded anddelayed. The signal thenpasses by way of the reproducing heads to thekey and the switch device. After leaving the sw tch device the signal isreceived in scrambled form and passes on to the transmission channel.When the apparatus is connected as a receiver the signal which is to bedeciphered passes through the switch device and the key to thetime-delay device and is recorded on the moving signal carrier in thecorrect order as regards time. The deciphered signal can thus be pickedup by the reproducing head located behind the m recording or reproducingheads and passed on to the receiver iii. The '01. heads of the apparatusshown in Fig. 8 thus function as reproducing heads when the apparatus isconnected as a transmitter, whilst when the apparatus is operating as areceiver they are used as recording heads. The arrangement shown in Fig.10 differs from that in Fig. 9 in so far as the signal is alwaysrecorded on the signal carrier in a ciphered form. In the transmitterthe signal thus passes to the switch device, arrives at the terminal illin a scrambled form and passes through the changeover device it to thetransmission channel l8. In the apparatus which is connected asareceiver the incoming scrambled signal goes first to the terminal F1 onthe time-delay device and arrives at the switch device deciphered. Withthe arrangements shown in Figs. 9 and 10 .it is of course assumed thatthe switch arms 5 (Figs. 6 and 8) in the apparatus I and II aresimultaneously on the same contacts, that is to say rotate in phase. Ifthe phase is the same in each case the sum of the running times from thehead 8 to the first head I and also those from the last head 1 to thehead i i are of no importance as regards the system of connections shownin Fig. 9. This is always the case when the signal is recorded on thesignal carrier in the transmitter and receiver in an unscrambled form.These additional running times must, however, be taken into account whenthe arrangement shown in I over device are shown in Fig.

Fig. 10 is used and they must then be so fixed that their total time isequal to one period of rotation of the switch device or a multiple ofsame. In each apparatus these running times are so fixed that each ofthem amounts to f times half the period of rotation of the switchdevice, 1 having such values as 0, 1, 2, 3, etc. In the practicalconstruction of the appara us it is essential to incorporate amplifiers.A comparison of Figures 9 and 10 shows that obviously three separateamplifiers should be employed, one

of which is either reversible or can be used for both-way transmission.with a steel tape timedelay device it is preferable to use only twoamplifiers for each apparatus, one amplifier serving exclusively foramplifying the signal reproduced I -corded signal cannot be obliteratedby simple means, this change-over system must be used under theconditions stipulated. The change-over from receiver to transmitter andvice versa is considerably simplified when signal carriers are employedwhere the signal can be erased by means of special wiping devices, suchas is the case with steel tape recording. In Fig. 8 the elements 8, Hand i5 are shown which according to the operating conditions function asreproducing, recording or wiping heads. When the head is used forrecording it is essential to have a supplementary direct current supplywhich is connected in series with the low-frequency recording circuitand produces a suitable initial magnetization of the steel tape. Thesame element can also be used as a wiping head if its coil is onlysupplied with direct current which produces a magnetization abovesaturation point and thus wipes out the recorded signal. When the headis used for reproducing purposes no additional voltage sources arerequired and the currents corresponding to the magnetic recording can bepicked up directly from the coil. Under these conditions the simplestform of changeover arrangement is obtained when the heads 8 and I Ishown in Fig. 8 are used alternately as wiping heads and the head l5either for recording or reproducing as thecase may be. Two suchapparatuses togetherwith the necessary change- 11 where the terminals 9and ill for the wiping heads and for the combined recording andreproducing head ii are indicated and the connections with theychange-over device l9 shown. This change-over device l9 connects thebattery shown in the drawing with either of the wiping head terminals 9or 10.. The remaining elements have the same reference numerals as inFigs. 9 and 10. In the position in which the change-over device i9 isshown in Fig. 11 the apparatus I functions as a transmitter and only thewiping head connected to terminal in removes the signal recorded on thesignal carrier, the wiping head connected to terminal 9 remaining out ofaction. In apparatus II which operates as a receiver the ar-- rangemeni;is reversed and only the terminal 9 is intermediate signal Zq byscrambling according elements are recorded on ti. to the first partialkey form of a variable magneti:

I I the first scrambling program 3 1 4 2 l I with the aid of one of thekeying devices already 3 1 4 2 described, this intermediate signal beingscramalready fixed in connection bled a second time by means of afurther keyintermediate signal Z accord ing device and according to thesecond partial ship (4) could now be pickei key head located on thesteel ta I, I ever, a number of receiving i 2 4 1 5 3 provided, whichare connects signals which are twice scrambled in this mints the key 81manner can be kept secret much better because switch segments the sewnin order to decipher them it i necessary to know g i that the Voltagesboth partial keys. According to the invention e colsi of theireceivmghea this advantage can be achieved with the use of :fi rece outgoing onetime-delay device K only because th unfinal signal (5) is new cipheredsignal is passed by means of the gz' Produced b1 switching devices Hiand H2 over the various o e in i Sig! pply and receiving organs to thesame timee secmd partial key delay device. The outlay for amplifiers,delay I I devices and the like i therefore considerably 2 4 1 5 3smaller than if two separat scrambling appa- The magnetic recording ier; ratuses are used and the noise level is also much head B, so thatthe steel ta improved. fresh recording. The key sysi Signals whichaccording to this method have f u 6 b eplaced by other been twicescrambled can be deciphered by means c nnecting the switch segmen: oftwo scrambling devices connected inv series, and receiving heads in anyde whereby the first device supplies the intermedi- A S l W h as been0111 ate signal Zq which is obtained from the signal e pp s o n in F g.13 Zz and the second device produces the original by means of anidentical appa signal Z1 from the intermediate signal Zq. In inglyadjusted and running syi accordance with the invention the signal can,reverse direction, the scramble however, be deciphered by using a singletimet oduced at terminal 2 and r4 delay device K to which the scrambledsignals at terminal I. In this second: are supplied through a firstswitching device and t pe h s oves past the heads taken off through asecond switching device. A similar apparatus .is illus The switchingprograms for both switching de- The magnetic steel tape is mou vicesmust of course correspond to the two para rotatin Wh ely means tialscrambling programs on the transmitting vice Hi. the signal Z1 which iside. A signal which has been ciphered by according'to a first partialkey means of the apparatus shown in Fig. 12 can for 110 the recording dsB11 to instance be deciphered by means of an identical the signal in theform of a, a apparatus when the ciphered signal is fed into 5 tiOn- Theelectric a es int the apparatus at the terminal 2 and the deof thereceiving heads B21 to ciphered signal picked up at the terminal I, theterminal 2 in the order determi signal elements which pass through theorgans Switch Hz. The magnetic reco. 2i to 25 to the time-delay K movingwith a speed means of the W p n head Bi 'u from right to left to thereceiving points i l to nected to a supply b e y thro Hi. When theswitching devices Hi and H2 on The appa a u h wn n F i the transmittingand receiving side respectively used for deciphering without 1 operatein synchronism and according to the the direction of rotation, if thesame program. then the signals passing the point is d in ou h th terminiq---.gy and fed into or picked up at the terminal i ciphered signaltaken oil at t] coincide on the transmitting and the receiving whichcase the switch R is cha side, that is to say the original signaltransmitted the wiping magnet .32 instead is obtained at the receivingend. operation. This simple ch: Fig. 13 shows a device whereby thesignal stor-' "scrambling, to deciphering' age is accomplished bymagnetic recording. A favourable when it is desired to steel tape c isdriven at a constant speed c by a transmission, because the sam motor Mpast the recording heads Bii to 314 the then be used'without any comreceiving heads 3321 to B25 and the wiping head B. over from transmitterto receivi The signal which is to be scrambled passes over being usedfor both directions 0 the ingoing terminal 8 to the switch Ui which is.The change-over switches U also driven by the motor M and connects theindescribed above can be so con. going conductor in turn with thevarious vertical tated that the time interval conductors of the firstkeying system A1. These switch positions of the switch verticalconductors are plugged in at the contacts interval T2 between two switchdetermined by the first key number so as to conswitch U2 is in bothcases equal. nect them with the diagonal conductors which suitable phaseadjustment for I lead to the coils of the recording heads B11 to B14. itis possible to arrange that thl According to the contacts plugged-in inFig. 13 a, b, c, (1, etc., whose length is connection is established inturn with 12, B11. recflrdlng are ot subd vided B and B12, that is tosay the individual signal picked up by the receiving he:

:y, the terminal I!) for the eing disconnected. The 6 remains unchangedand l to the terminal ,4 of the apparatus. As in the case ted in Fig. 9the suppleiing time in each apparalce because obviously the the steeltape in an un- 1 the arrangement; shown a very simple matter to over theamplifiers if only vided one of which serves the alternating currentdcked up. The amplifiers up either in front of the he terminals 4,depending are intended to serve..

illustrated in Figs. 6+11 identical apparatuses are arating a steel tapetime- .he disadvantage that the ed must be recorded and mes. When forinstance ltuses are employed it is vide three separate steel therdevelopment of the en possible to avoid this 1e same time retain all theiltipl scrambling system. is the signal elements the o be scrambled inaccordiodically recurring partial different supply organs iese organsbeing characrunning times, and the re picked up through difs of the samestorage de- .th a second partial properiodically different inorgansbeing also characinning times. Thus it is successive partial scram-Eerent programs with the :e device and without too' ng necessary.

ambling is now explained the constructional exam- 12-15 of theaccompanyants the first switching deh the ingoing conductor l varioussupply leads I l, -delay device K in accordremains the sam from group togroup.

al program. In the time-- a1 elements move with a the various supplypoints A second switch dethe outgoing conductor 2 partial program withthese Jresent the length with re- I icoming and outgoing elelat is tosay-the interval switch segments of the switch devices H1 and H2. Sincethe unused incoming and outgoing organs can be omitted it is alsopossible that the distance between two remaining adjacent leads mayamount to an integral multiple of D1 or Dz respectively. 1

The signal to be scrambled Z1=abcdefghiklm (3) consisting of the"elements a, b, 0, etc, each of equal length, is now passed to theincoming conductor I. For instance four successive elements of thissignal form a group, the switching-over in H1 being accomplished in asequence which Ac-- cording to a first four-figure key theswitching-over should for instance occur in such a manner that thesignal elements which travel with a speed 22 from left to right throughthe time-delay device pass the point q-q in the following order: Thefirst element a will now occupy the third place in accordance with thekey number 3, the second element 1) as result of the second key numberprovided with a stroke couples the (1+4) =fifth place, the third element0 as a result of the third key number 4 occupies the fourth place andthe fourth element lies as a result of the key number in the (2+4)=sixth place. The elements of the second and following groups aredelayed in an analogous manner. This is achieved by connecting theingoing conductor i in turn by means of the switching device Hi with thesupply organs ll, I2, l3, etc. The signal elements pass ing the point qqrepresent a first partial scrambling of the original signal Z1. If aspecial receiving device were located at the point q-q .it would thus bepossible to picls up the scrambled signal:

Z a.c bdegfhillcm... (4)

The signal which has been subjected to simple scrambling is, however,not picked up at this point but taken from the device K through thereceiving organs 29 to 25 and the switching de vice Hz after a furtherscrambling. The signal is taken from the time-delay device for in stanceaccording to a second key organs 24, 22, 2d, 23, 22. Instead of thesignal Z11 the following signal is received at theterminal 2, thissignal result- 'ing from "a double scrambling of the original ingoin'gsignal Z1. The signal Z2 is thus produced from the signal Z1 by firstobtaining the scrambled signal Z2 also consists of such elements a, b,c, d, etc., and not fractions of same. This condition has been assumedfor instance in connection with the description given of the arrangementshown in Fig. 12 but must not always be so. The length of the elementsdetermined by the switch U1 can, however, be subdivided by the switch U2if this latter is rotated with a difi'erent phase position or operateswith a time interval T2 which differs from T1. Even in such a case it isof course possible to decipher the signal which has been scrambledaccording to the method described, if the change-over devices at thereceiving end operate with corresponding phase adjustment andchange-over frequency.

In order to increase the secrecy of transmission the apparatus accordingto the invention can be connected in series with other scramblingdevices so that a multiple scrambling system is formed. The easiest andsimplest form of multiple scrambling system can be obtained if severaldouble-scrambling systems of the kind described above are connected inseries. In Fig. an arrangement with two double-scrambling apparatuses E1and E2 connected in series and having an intermediate amplifier v, isshown diagrammatically. If the apparatuses E1 and E2 are such that whenthe direction in which the signal passes through the device is reversedthe signal is deciphered, the arrangement shown in Fig. 15 can be usedeither for scrambling or deciphering as desired, the signal passingeither from left to right or vice versa. To correspond to the directionin which the signal is being transmitted it is essential to change overthe connections of the amplifier v by means of the switches R1 and R2.

When a number of scrambling systems are connected in series it isadvisable to employ apparatus in which the period of rotation of theswitches difiers from each other so that the complete scrambling programrepeats itself after time intervals which are longer than the period ofrotation of the individual scrambling devices, unauthorized decipheringbeing thus made considerably more dificult.

The magnetic time-delay device shown-in Figs. 13 and 14 can of course bereplaced by other known kinds of time-delay devices. The device K inFig. 12 can for instance consist of a tubular acoustical retardingdevice with suitable loudspeaker systems located atthe supply points Hto l4 and microphones at the picking-up points 2i to 25. It is alsopossible to use an electrostatic recording system with a movinginsulated member or optical recording combined with photo-electric cellsfor picking up the signal ele- 'ments by means of a variable transparentsignal carrier. v

The switch devices for the variable recording and receiving of thesignal elements can consist of electrically operated mechanical switcheswith sliding contacts or cam contacts. The ingoing and outgoingconductors to the recording and receiving heads can, however, also beprovided with electric valves which are electrically controlled inaccordance with a fixed program. For this purpose dry rectifiers orelectron tubes can for instance be used, these being renderedintermittently conductive by means of short control impulses. Theswitching-over process can also be accomplished by means of cathode raytubes the ray of which is diverted by a number of mutually insulatedelectrodes which are connected in the desired sequence with the variousrecording and receiving organs of the time-delay device.

We claim:

1. A method of sending and receiving signals in cipher which comprisessubjecting a signal in succession to a plurality of substantiallycontinuous time-delayed scrambling operations in each of which the orderof elements of the signal is transposed in accordance with a preselectedrecurrent program to produce a multiscrambled signal, transmitting themultiscrambled signal, and subjecting the received signal to a pluralityof successive, substantially continuous scrambling operationscorresponding in number to the number of scrambling operations and ineach of which the order of elements of the signal is transposed ininverse relation to the transposition efiected in the inverselycorresponding scrambling operation.

2. A method of sending and receiving signals in cipher whichcomprisessubjecting a signal in succession to a plurality ofsubstantially continuous time-delayed scrambling operations in each ofwhich the order of elements of the signal is transposed. in accordancewith a preselected periodically recurrent program, the number of signalelements in the period of said recurrent programs being difierent ineach successive scrambling operation, to produce a multiscrambledsignal, transmitting the multiscrambled signal, and subjecting thereceived signal to a plurality of successive, substantially continuousunscrambling operations corresponding in number to the number ofscrambling operations and in each of which the order of elements of thesignal is transposed in inverse relation to the transposition effectedin the inversely corresponding scrambling operation.

3. A method of sending and receiving signals in cipher which comprisessubjecting a signal in succession to a plurality of substantiallycontinuous time-delayed scrambling operations in each of which thesignal is divided into a plurality of signal elements of equal lengthwhich elements are then transposed according to a preselectedperiodically recurrent program to produce a multiscrambled signal, thenumbers of elements comprised in the recurrent periods of eachscrambling operation having no common factor other than unity,transmitting the multiscrambled signal, and subjecting the receivedsignal to a plurality of successive, substantially continuous,unscrambling operations corresponding in number to the number ofscrambling operations and in each of which the order of elements of thesignal is transposed in inverse relation to the transposition eii'ectedin the inversely corresponding scrambling operation.

4. A method as defined in claim 1 in which the length of the signalelements of one scrambling operation is an integral multiple of thelength of the signal elements in another scrambling operation and inwhich the periodicity of the program of said one scrambling operationdiffers from the periodicity of the program of said other scramblingoperation.

5. A method as defined in claim 1 in which the length of signal elementsof any one of the scrambling operations bears no rational relationshipto the length of the signal elements of any other of the scramblingoperations.

6. In a secret signalling system in which 59-- crecy is obtained by'transposing components of the signal to produce a scrambled signal fortransmission, the method which comprises sub- Jecting the signal to aplurality of scrambling operations in succession, each scramblingoperation including the division of the signal into a plurality ofelements and the elements of successive scrambling operations being ofdiflerent magnitude.

7. In a secret signalling system in which secrecy is obtained bytransposing components of the signal to produce a scrambled signal fortransmission, the method which comprises subjecting the signal to a,time-delayed scrambling operation in which the individual signalelements of recurrent groups of signal elements we transposed .toproduce a scrambled intermediate signal, and subjecting the scrambledintermediate signal to at least one additional scrambling operation.

8. A method of sending and receiving signals in cipher which comprisesdividing the signal on a time basis into recurrent groups of signalelements, subjecting the several elements of each group to unequaltime-delays to develop a scrambled intermeoiate signal in which theorder of the elements of each group is transposed in accordance with apreselected program, dividing the scrambled intermediate signal intorecurrent groups of signal elements, subjecting the several elements ofeach group of the scrambled intermediate signal to unequal time delaysto develop a multiscrambled signal, transmitting the multiscrambledsignal, subjecting the transmitted multiscrambled signal to anunscrambling operation to produce a received intermediate signalduplicating the scrambled intermediate signal, and subjecting thereceived intermediate signal to an unscrambling operation to produce aduplicate of the original signal.

9. Apparatus for sending and receiving si nals in cipher including atransmitter and a receiver, said transmitter comprising a plurality ofscrambling devices through which the signal is transmitted in sequence,each of which scrambling devices includes means for dividing the signalinto a plurality of elements and means for transposing said signalelements according to a preselected recurrent program, said receivercomprising a plurality of unscrambling devices equal in number to thenumber of scrambling devices of the transmitter and through which thesignal is passed in sequence, each of said unscrambling devicesincluding means for dividing the signal into a plurality of elements andmeans for transposing said signal, elements in inverse relation to acorresponding scrambling device of the transmitter, said unscramblingdevices being arranged in inverse order to said scrambling devices withrespect to the direction of signal travel therethrough, and means forsynchronizing the operation of said transmitter and said receiver,whereby the signal is scrambled in the transmitter, transmitted inscrambled form, and unscrambled in the receiver to reproduce theoriginal signal.

10. A device for scramblirm and unscrambling a signal which comprises acontinuous signal carrier, a substantially continuously operating timingdevice for dividing a, signal in transit on said signal carrier intorecurrent groups of signal elements, means for conducting signalelements between a plurality of positions on said signal carrier and aplurality of sections of said signal divider, thereby providing aplurality of paths between each of said positions and each'of saidsections, and means for selecting a unique path between a carrierposition and a divider section for each successive signal element in apredetermined group of elements.

11. A device for scrambling and unscrambling a signal which comprises amagnetizable tape, switch means for dividing a signal into a pluralityof elements in accordance with a preselected program, a plurality of'electromagnets 1n magnetizing relation to said tape, means for conducting signal elements between a plurality of sections of said switchmeans and said plurality of electromagnets, said conducting meansproviding a plurality of paths between each of said sections and each ofsaid magnets, means for selecting a unique path between a section ofsaid switch means and a magnet for each successive signal element in apredetermined group of elements, and means for translating said tapepast said magnets.

12. A device as defined in claim 11 wherein the means for conductingsaid signal elements between said switch means and said electromagnetsincludes a network of two groups of conductors of which one groupcomprises leads from the several terminals of the switch means and theother group comprises leads from said plu-,

rality of electromagnets and said selector means includes means forconnecting any of the first group of leads with any of the second groupof leads.

13. A device as defined in claim 11 in which said switch means is arotating switch for dividing the signal into' a plurality of equallylong elements, said magnetizable tape is endless and is translated atconstant velocity, said electromagnets are equally spaced along saidtape, and in which a common driving means is provided for rotating saidswitch and for translating said tape according to the followingrelationship in which n is the number of switch elements of said switchmeans, d is the distance between adjacent electromagnets, 12 is thevelocity of said tape, 8 is the period of rotation of said switch means,and p is any positive integer, said endless tape being further providedwith means for obliterating magnetic impressions thereon at each cycleof the tape.

14. A device as claimed in claim 11 wherein said switch means includes aplurality of switch elements each comprising opposed contact springs,said switch elements being actuated in sequence by a rotating cam drivenin timed'relation to the velocity of translation of said tape.

15. A device for scrambling and unscrambling a signal which comprises acontinuous signal carrier, a substantially continuously operating signaldivider, means for conducting signal elements between a plurality ofpositions on said signal carrier and a plurality of sections of saidsignal divider, said conducting means providing a. plurality of pathsbetween each of said positions and each of said sections, means forselecting a umque path between a carrier position and a divider sectionfor each successive signal element in a predetermined group of elements,a second substantially continuously operating signal divider having adifferent number of sections than said first mentioned signal divider,means for conducting signal elements between said plurality of positionson said signal carrier and a plurality of sections of said second signaldivider, said second conducting means providing a plu'-' rality of pathsbetween each of said positions and each of said sections, and a secondmeans for selecting a unique path between each of said positions andeach of the sections of said second signal divider for each successivesignal element in a predetermined group of elements.

16. A device for scrambling and unscrambling a signal which comprises amagnetic tape, switch means for dividing a signal into a plurality ofelements in accordance with a preselected program, a plurality ofelectromagnets in magnetizing relation to said tape, means forconducting signal elements between a plurality of sections of saidswitch means and said plurality of electromagn'ets, thereby providing aplurality of paths between each of said sections and each of saidmagnets, means for selecting a unique path between a section of saidswitch means and a magnet for each successive signal element in a.predetermined group of elements, a second substantially continuouslyoperating switch means having a different number of sections than saidfirst mentioned switch means, a second plurality of electromagnets inmagnetizing relation to said tape, means for conducting signal elementsbetween a plurality of sections of said second switch means and saidsecond plurality of electromagnets, thereby providing a plurality ofpaths between each of said sections and each of said magnets, a secondmeans for selecting a unique path between a section of said secondswitch means and one of said second plurality of magnets for eachsuccessive signal element in a predetermined group of elements, andmeans for translating said tape past said two groups of electromagnets.

1'7. A device as defined in claim 16 in which the means conducting thesignal elements between each'switch means and its respective pluralityof electromagnets includes a network of two groups of conductors ofwhich one group comprises leads from the several terminals of the switchmeans and the other group comprises leads from the plurality ofelectromagnets and means for connecting any of the first group of leadswith any of the second group of leads.

18. A device as defined in claim 16 in which a common source of poweris'provided for driving said switches and said tape in preselected timedratio, and in which said tape is endless.

19. A device as defined in claim 16 in which said magnetizable tapecomprises the periphery of a rotating wheel, said sets of electromagnetsbeing disposed about the periphery, and in which means is providedbetween said sets of electromagnets for obliterating magneticimpressions upon said tape.

20. A device as defined in claim 16 in which both of said switch meansinclude electrically controlled valves for controlling the transmissionof the signal elements to the different sections of said switch means. I

GUSTAV GUANELLA. WALTER ERNST. WERNER LINDECKER MARCEL GABRIEL.

